The present invention relates to a structured packing having particular application to a method of separating air in which the packing is formed of a plurality of corrugated sheets and a plurality of flat, planar members alternating with and located between the corrugated sheets to inhibit vapor turbulence. More particularly, the present invention relates to such a structured packing in which the corrugated sheets and the flat, planar members have perforations sized to inhibit vapor and liquid flows but to allow for pressure equalization through the packing.
Structured packing has found wide spread use in a variety of distillations including those involved in the separation of air into its component parts. Distillations are conducted within distillation columns filled with mass transfer elements to bring ascending vapor phases into intimate contact with descending liquid phases of mixtures to be separated. As the ascending phase rises and contacts the descending liquid phase, it becomes evermore enriched in the more volatile components of the mixture to be separated. At the same time the descending liquid phase becomes ever more concentrated in the less volatile components of the mixture to be separated. In such fashion, systems of distillation columns can be used to separate various mixture components. For instance, in case of air separation, nitrogen is separated from oxygen is a double distillation column unit. Argon is then separated from oxygen in an argon column that is attached to a lower pressure column of such double distillation column unit.
Structured packings are widely used as mass transfer elements within distillation columns due to their low pressure drop characteristics. Structured packings generally include corrugated sheets of material in which the sheets are placed in a side by side, relationship with the corrugations of adjacent sheets crisscross-crossing one another. In use, the liquid phase of the mixture to be separated is distributed to the top of the packing and spreads out throughout the packing as a descending film. The vapor phase of such mixture rises through the corrugations contacting the liquid film as it descends.
There have been many attempts in the prior art to increase the efficiency of structured packings, that is, to decrease the height of packing equal to a theoretical plate. Obviously, the lower the height, the more efficient the packing. At the same time, structured packing with a low HETP inherently has an increased pressure drop over less efficient packings. One such structured packing is disclosed in U.S. Pat. No. 4,597,916 in which the corrugated sheets are separated from one another by flat, perforated sheets that extend throughout the packing. It is thought by the inventors herein that the flat perforated sheets of this packing increase efficiency both by providing additional interfacial area for vapor-liquid contact and by increasing turbulence in the vapor flow and therefore the degree of mixing between vapor and liquid phases. Transverse mixing is also increased by perforations that are specifically designed to promote liquid and vapor flow in a transverse direction of the packing.
As will be discussed, Applicants have designed a structured packing that unlike the prior art, is optimized not for efficiency, but rather, for smooth vapor flow. Through such optimization, the Inventors herein have found that it is possible to increase the capacity of the packing and therefore, use such packing in a more efficient cost effective manner.